A photo posted by @ittybittyphotographytas on May 24, 2016 at 3:45am PDT

RIGHT up until the moment she gave birth, Koto Nakamura was certain of her baby's gender. According to her ultrasounds, she was having a girl.

So when the Tasmanian first-time mother learnt she had in fact just given birth to a boy, she was in total shock and her priceless reaction was caught on camera by birth photographer Jessica Jackson.

According to Jackson, during Nakamura's delivery the midwife shared what turned out to be an uncanny story about a past client who had been told her baby was one gender, and then gave birth to the opposite.

Moments later Nakamura was experiencing the same thing. Jackson told kidspot.com.au that Nakamura thought she hadn't heard correctly when she was told her baby was in fact a boy.

"She was saying, 'not Hinata?'" said Jackson.

Nakamura and her partner, Sina Niakansafy, had prepared for the arrival of a baby girl, choosing the name "Hinata".

But Jacson said once the surprise sunk in, the couple were "beyond excited" with Niakansafy "planning camping trips with his son".

A photo posted by @ittybittyphotographytas on May 24, 2016 at 3:15pm PDT

Jackson, who has been a birth photographer for four years, knew she had captured a special shot, but was concerned it wasn't going to be in focus because of "all the excitement and laughter" surrounding the moment.

"I got to really experience the highs and lows in that delivery room and capture all of that for them to look back on," said Jackson, who was invited to spend the day with the family - including Nakamura's mother who came especially from Japan - to be a friend and support as well as photographer.

Sharing the image to Instagram, Jackson wrote: "The priceless look on a mamas face who was told she was having a baby girl but received a baby boy!! Talk about a big surprise!!"

The couple have called their son Taiga, a Japanese name meaning "big and gracious."